1. Field of the Invention
This invention relates to high-Tc superconducting lead assemblies in a cryostat dual penetration for refrigerated superconductive magnets. Such structure of this type, generally, provide electrically isolated current paths with minimal heat leak between the 10K thermal station and the 50K thermal station while allowing for differential thermal contraction in the assembly, thus avoiding undesirable stresses in the leads.
2. Description of the Related Art
It is known in prior refrigerated superconductive magnets to use a cryorefrigeration system which employs a single cold head. The major limitation of these system is the fact that if the single cold head malfunctions, the superconductive magnet may not be properly cooled, which could adversely affect the performance of the magnet. In short, the system typically was only as reliable as the cryorefrigerator itself. Therefore, a more advantageous system would be presented if this unreliability were reduced or eliminated.
In order to increase the reliability in refrigerated superconductive magnet systems, a redundant cold head system for a refrigerated magnet has been developed. Exemplary of such prior redundant systems is U.S. Pat. No. 5,111,665 ('665), to R. A. Ackermann, entitled "Redundant Cryorefrigerator System For a Refrigerated Superconductive Magnet", now allowed and assigned to the same assignee as the present invention. In the ('665) application, one cold head of the two used in the system cools the magnet. A redundant cold head does not contact the magnet and is held in a raised, standby position. If the main cold head malfunctions, the main cold head is raised so that it can be repaired, serviced or replaced and the redundant cold head is lowered to contact the magnet. In this manner, the cooling of the magnet should be substantially continuous. While this cryorefrigeration system has allowed the magnet to be run continuously, further reductions in the amount of vibration reaching the magnet would be achieved if the cold heads were not rigidly attached to the magnet. Vibration in the magnet is not desired because the vibration can cause artifacts in the image produced by the magnet. Consequently, further reductions in the vibration in the magnet while continuously cooling the magnet would be advantageous.
In the ('665) application, current leads are thermally connected to the thermal shield so that heat conducting down the leads from ambient temperature is intercepted at the first thermal station. Further reductions in the amount of heat conducting down the current leads between the thermal shield and the second thermal station would be advantageous.
It is apparent from the above that there exists a need in the art for a high-Tc superconducting lead assembly which minimizes the heat conducting down the leads from the first thermal station to the second thermal station and which is capable of allowing the magnet to operate continuously, but which at the same time substantially prevents thermal stresses from adversely affecting the leads. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.